Planes don't show assigned colors/ images
The problem:
You are using the Compositor Editor.
This will never work, you need to use the Shader Editor.

How to:
1) Open the Shader editor.
2) Select your object and click the + New button, to add a new material.
3) Add an Image texture node and select your image.

Open your Shader editor.
With your object selected, click the New material button.


Add the Image Texture node, and connect it like this.
Then click Open and find your image texture.


This is the result.
If you want to see it, you need to be in the Material Preview or Rendered Preview.




If you're a beginner, I wholeheartedly reccomend BlenderGuru's Donut tutorial series for beginners.
Spend some time there, and you'll learn much more :).

Good luck! :)